The invention relates to a process and machine for fine machining of geared workpieces with a driven toothed wheel or worm-thread tool which is meshing contact with a workpiece, the axes of tool and workpiece intersecting.
A machine of this type has been described in U.S. Pat. No. 4,950,112 to Huber. In this state-of-art machine there are mounted on the bench two tailstocks which receive between them a geared workpiece to be machined in such a way that this workpiece is rotatable about a horizontal axis. This state-of-the-art machine operates in the so-called free-running process, that is, the tool drives the workpiece in free running by way of tooth contact between tool and workpiece. Various state-of-the-art shaving processes determined by the equipment of the machine, such as plunge shaving, parallel shaving, diagonal shaving, or underpass shaving, are possible. The machining process is interrupted for workpiece replacement, that is, the tool and the workpiece come to a standstill, the chucking equipment is released, the machined workpiece is removed, and a non-machined workpiece is mounted (tooth engagement), the chuck is tightened, and the workpiece is set in motion by the tool.
Machining begins, after mounting of the workpiece in the stationary tool, with acceleration of the tool to operating speed and ends with braking of tool and workpiece before removal of the latter. The direction of rotation must be reversed during machining to prevent uneven machining of the tooth flanks which otherwise results from the forces of inertia and friction which exert their effect. In addition, the surface of the tooth flanks may be affected in this manner. Additional pauses are integrated into the machining process for these reasons. Up to the present the process has been conducted with constant, freely selected tool feed rates and at constant operating speeds (except for the acceleration and braking processes), it being possible to assign several different values within the machining process. After the assigned speed has been reached, the workpiece is moved to a clearly defined axial spacing position by rapid feed motion. Additional feed motion between tool and workpiece during machining is then effected in one or more selected feed steps. At a selected axial spacing position the advance may first be stopped but machining at rated speed may be continued for the duration of a first shaving period (pause before reversal). The tool is then slowed down, its direction of rotation is changed, and it is again accelerated to its preselected speed of rotation. After this speed has been reached, repositioning to the assigned axial spacing is made. In this so-called zero position a new shaving period (pause in zero position) is introduced. This is followed by a brief backstroke (so-called Wich period) which has the effect of smoothing the flank surface. The choice of the individual advance values, speeds, direction of rotation, and shaving period constitute the only potential influence on the result of shaving within the process. After the Wich period the tool is braked to a standstill and the workpiece is disengaged. After the machined workpiece is removed and a new workpiece is placed in position, the machining process described above is restarted.
It is an object of the present invention to improve the generic machining process with respect to productivity and quality.
The object of the present invention is attained in that the tool is driven in a direction which remains the same during machining of the workpiece, and in that adjustable torque values are imparted to the workpiece in one direction and then in the opposite direction. The torque values imparted to the workpiece, which are optional with respect to magnitude and direction, make it possible to simulate the forces of inertia and friction previously modified by reversal of the direction of rotation of the driven tool and to save the time taken up by this component.
Additional time can be saved by accelerating the workpiece to operating speed and bringing it into contact with the rotating tools. Doing so eliminates the previous time components required for acceleration and deceleration of workpiece and tool while in contact. Consequently, the tool may rotate without interruption.
The torque values imparted to the workpiece may also be used specifically to affect machining of the workpiece and to improve the results of machining. Pitch and runout of the workpiece, for example, may be affected by imparting a particular torque value to the workpiece. This has not previously been possible in gear wheel shaving with a free running workpiece.
The invention also is directed to a machine for application of the inventive process. The machine comprising a bench, a first slide which is mounted on the bench so as to be movable and which may be driven in movement along a first axis X, a second slide which is mounted on the first slide so as to be movable and may be driven in movement along a second axis Z at a right angle to the first axis X, a tool head which is pivotably connected to the second slide and which is pivotable about a third axis A parallel to the first axis X for adjustment of the angle of intersection between tool and workpiece, a motor mounted on the tool head for powering a tool spindle, and a tool spindle with chucking equipment for clamping a workpiece.
A preferred embodiment of the invention is described in detail below with reference to the attached drawings.